The present disclosure relates to solid oxide fuel cells, and particularly to a gas diffusion mat for fuel cells.
A fuel cell is an energy conversion device that converts chemical energy into electrical energy. The fuel cell generates electricity and heat by electrochemically combining a gaseous fuel, such as hydrogen, carbon monoxide, or a hydrocarbon, and an oxidant, such as air or oxygen, across an ion-conducting electrolyte. The fuel cell generally consists of two electrodes positioned on opposite sides of an electrolyte. The oxidant passes over the oxygen electrode (cathode) while the fuel passes over the fuel electrode (anode), generating electricity, water, and heat.
A solid oxide fuel cell (SOFC) is constructed entirely of solid-state materials, utilizing an ion conductive oxide ceramic as the electrolyte. A conventional electrochemical cell in a SOFC is comprised of an anode and a cathode with an electrolyte disposed therebetween. Typically, the components of an electrochemical cell and a SOFC are rigid and extremely fragile since they are produced from brittle materials.
In a typical SOFC, a fuel flows to the anode where it is oxidized by oxide ions from the electrolyte, producing electrons that are released to the external circuit, and mostly water and carbon dioxide are removed in the fuel flow stream. At the cathode, the oxidant accepts electrons from the external circuit to form oxide ions. The oxide ions migrate across the electrolyte to the anode. The flow of electrons through the external circuit provides for consumable or storable electricity. However, each individual electrochemical cell generates a relatively small voltage. Higher voltages are attained by electrically connecting a plurality of electrochemical cells in series to form a stack.
Seals must be provided around the edges of the various cell stack components to inhibit cross-over of fuel and/or oxidant. For example, seals are disposed between the electrodes and adjacent flow fields, around manifolds, between flow fields and cell separators, and elsewhere. One factor in establishing SOFC reliability is the integrity of these seals. Leaks in the manifold seals, electrochemical seals, or other defects can lead to the SOFC failure. When oxygen crosses over to the anode, forming an oxidizing environment, anode oxidation can occur, creating a volume change that results in an increase in internal stress and ultimately in a costly mechanical failure of the electrochemical cell. Thus, many failures can be attributed to the rigidity of the SOFC.
What is needed in the art is a more flexible and, hence, more durable SOFC.
The drawbacks and disadvantages of the prior art are overcome by the solid oxide fuel cell, solid oxide fuel cell stacks, and interconnect disclosed herein. The interconnect comprises an expander and a flow section disposed between the expander and an interconnect periphery.
In one embodiment, the solid oxide fuel cell comprises an electrolyte disposed between and in ionic communication with a first electrode and a second electrode to form an electrochemical cell. Disposed in physical contact with at least a portion of the electrochemical cell is a mat, with a spacer disposed around the mat.
Another embodiment of the solid oxide fuel cell stack comprises at least two solid oxide fuel cells. Each solid oxide fuel cell comprises an electrolyte disposed between and in ionic communication with a first electrode and a second electrode, forming an electrochemical cell. A mat is disposed adjacent to and in physical contact with at least a portion of the electrochemical cell, with at least one spacer disposed around the mat. On the side of the mat opposite the electrochemical cell is an interconnect.
One method for manufacturing an embodiment of the solid oxide fuel cell stack, comprises disposing an electrolyte between and in ionic communication with a first electrode and a second electrode to form an electrochemical cell. A mat is disposed in physical contact with at least a portion of the electrochemical cell. Around the mat, at least one spacer is disposed. Disposed in electrical communication with the mat, on a side opposite the electrochemical cell, is an interconnect.
In one embodiment, the solid oxide fuel cell stack comprises at least two solid oxide fuel cells. The fuel cells comprise an electrochemical cell formed of an electrolyte disposed between and in ionic communication with a first electrode and a second electrode. Disposed between adjacent fuel cells is an interconnect having at least one flow section disposed between an expander and a periphery.